This invention relates to applying a braking force to a rotor, and more particularly to a disc brake caliper of the type used in vehicles.
In a typical disc brake apparatus for a vehicle having wheels, such as an automobile a truck, or a motorcycle, a disc brake caliper apparatus attached to a frame of the vehicle is used for applying braking force to the sides of a rotor attached to one or more of the wheels of a vehicle. The calipers used presently, however, do not fully disengage from the sides of the rotor between applications of braking force. Brake linings of the caliper remain in contact with the sides of the rotor creating a drag force on the rotor that reduces fuel economy of the vehicle.
As shown in FIG. 1, a typical disc brake apparatus 10 includes a rotor 12 and a brake caliper 14 attached to a common support 16, such as a steering knuckle, or the chassis of a vehicle. The rotor 12 is mounted for rotation with a wheel of the vehicle, about a rotor axis 18 coincident with the axis of the axle about which the wheel rotates.
The caliper 14 includes a caliper housing 20 that is slidably mounted on a pair of mounting pins 22 to the support 16, in a manner that allows the caliper 14 to move a short distance toward or away from the support 16, during operation of the brake 10. A flexible dust boot 24 is provided around the pins 22 in the space between the housing 14 and the support 16.
The housing 20 includes a circumferential shaped slot 26 that fits over a portion of the periphery of the rotor 12, and to provide clearance for a pair of brake shoes 28, 29 having linings 30 positioned to be clamped against an inboard and an outboard side 32, 34 of the rotor 12. The brake shoes 28, 29 are suspended on the pins 22 in a manner that lets the shoes 28, 29 slide on the pins 22. Tabs 46, 48, and 50 on the brake shoes 28, 29 transfer the braking loads to the housing 20 during vehicle braking.
The caliper 14 also includes a piston 36 mounted in a cylinder bore 38 to be movable along a bore axis 40 for moving the inboard brake shoe 28 into contact with the inboard side 32 of the rotor 12, for applying a braking force against the inboard side 32 of the rotor 12, when pressurized fluid is introduced into the cylinder bore 38 in a space 42 behind the piston 36.
As the piston 36 applies braking force to clamp the inboard brake shoe 28 against the inboard side 32 of the rotor 12, the pressurized fluid in the space 42 in the cylinder bore 38 behind the piston 36 causes the housing 20 to move in an opposite direction along the bore axis 40. This movement of the housing 20 pulls the outboard lining 30 of the outboard brake shoe 29 into contact with the outboard side 34 of the rotor 12, creating a clamping effect, so that the motion of the piston 36 toward the inboard side 34 of the rotor 12 applies braking force to both the inboard and outboard sides 32, 34 of the rotor 12.
When fluid pressure is released in the space 42 behind the piston 36, the piston 36 is retracted a few thousandths of an inch by the action of a specially designed seal 44, between the cylinder bore 38 and the piston 36, in a manner known in the art. With the piston 36 retracted, the inboard brake shoe 28 is free to move away from the inboard surface 32 of the rotor 12.
There is no mechanism provided, however, for moving the outboard brake shoe 29 away from the outboard side 34 of the rotor 12. This results in undesirable drag between the lining 30 on the outboard shoe 29 and the outboard side 34 of the rotor 12, thereby reducing fuel economy of the vehicle to which the brake 10 is attached.
In addition, because the caliper 14 and the brake shoes 28, 29 must slide on the pins 22, and yet still be capable of withstanding braking loads transferred to the caliper housing 20 by the tabs 46, 48, and 50 on the brake shoes 28, 29, for proper operation of the brake 10, the caliper housing 20 is a complex shape, and is typically produced by an expensive process such as casting the housing from iron or steel, and carrying out complex machining operations to bring the housing to its final shape. Caliper housings 20 of the type used in the past are also heavy.
What is needed, therefore, is an improved disc brake apparatus providing a solution to one or more of the problems and disadvantages described above.
The invention provides an improved braking apparatus for applying a braking force to the inboard and outboard sides of a brake rotor, through the use of a pair of pistons disposed in a back-to-back relationship in a cylinder bore of a housing, and defining a space between them in the cylinder bore for receipt of a pressurized fluid.
In one form of the invention, the rotor is rotatable about a rotor axis, and the cylinder bore defines a bore axis extending parallel to the rotor axis. A first piston of the pair of pistons is slidably disposed in the cylinder bore for movement in a first direction along the bore axis toward the inboard side of the rotor for applying a braking force to the inboard side of the rotor, and the second piston of the pair of pistons is slidably disposed in the cylinder bore for movement in a second direction opposite the first direction along the bore axis for applying a braking force to the outboard side of the rotor.
A braking apparatus, according to the invention, may further include a movable bridge element slidingly attached to the housing for transmitting a braking force from the second piston to the outboard side of the rotor.
The invention may also take the form of a method for applying a braking force to the inboard and outboard sides of a brake rotor by connecting a first piston and a second piston disposed in a back-to-back relationship in the cylinder bore and defining a space between them in a cylinder bore for receipt of a pressurized fluid, to the inboard and outboard sides of the rotor, and introducing a pressurized fluid into the space between the first and second pistons, so that the first and second pistons generate a braking force applied to the first and second sides of the rotor.